Superconductive devices



bept. 6, 1966 J. vv. cRoWE .SUPERCONDUCTIVE DEVICES 4 Sheets-Sheet lOriginal Filed Aug. 27, 1957 SUBSTRATUM FIG.3

INVENTOR.

JAMES W. CROWE TTORN EY I I l Sept 6, 1966 I J. w. CROWE 3,271,585

SUPERCONDUCTIVE DEVI CES original Filed Aug. 27, 1957v 4 sheets-sheet 2VANADIUM 800 700 LEAD-INDIUII Coo 50@ I=IC.4 HC (GAUSS) 400 300MERCURT?\\ 20o THALLIUM IOC X o I 2 5 4 5 e 7 TIDECREES KI soo CooCRITICAL CURRENT 500 F|G 5 (MILLIAMRS) 400 Y 20o X Ioo` TIDECREES KIRESISTANCE C1 C I COMBINED MAGNETIC FIELD AND TEMPERATURE J. W. CROWESUPERCONDUCTIVE DEVICES Sept. 6, 1966 4 Sheets-Sheet 3 Original FiledAug. 27, 1957 9 Vu F Sept. 6, 1966 J, w, CROWE 3,271,585

SUPERCONDUCTIVE DEVICES Original Filed Aug. 27, 1957 4 Sheets-Sheet 4 SUBSTRATUM /7 f3 /8 12 l 5 S1] /f/ k /f//f j SUBSTRATUM K L 1 UnitedStates Patent O 2 Claims. (Cl. 307-885) This invention relates toelectrical devices, and particularly to those devices employingsuperconductors.

This application is a division of patent application Serial Number848,870, led October 26, 1959, which application Serial Number 848,87()is a continuation of patent application Serial Number 680,456, filedAugust 27, 1957 now abandoned.

The properties and characteristics of superconductors have been treatedin such texts as Superiiuids, volume I by Fritz London, published in1950 in New York by John Wiley & Sons, Inc. and Super-conductivity by D.Shoenberg, published in 1952 in London by the Cambridge UniversityPress. In general, a superconductor is a metal, an alloy or a compoundthat is maintained at very low temperatures, i.e., from 17 K. to thepractical attainability of absolute zero, in order that it may presentno resistance to current flow therein. It was discovered that in thecase of mercury its electrical resistance decreased as a function ofdecreasing temperature until at a given temperature (about 412 K.) theresistance very sharply vanished, or its measurement was too small to bedetected. The temperature at which the transition to Zero resistancetook place in mercury was referred to as its critical temperature; itsstate, upon reaching zero resistance, was that of a superconductor.

The critical temperature varies with different materials, and for eachmaterial it is lowered as the intensity of the magnetic field around thematerial is increased from Zero. Once a body of material is renderedsuper-conductive, it may be restored to the resistive or normal state bythe application of a magnetic field of a given intensity to suchmaterial; the magnetic iield necessary to destroy superconductivity iscalled the critical iield. Thus it is seen that one may destroysuperconductivity in a specific material by applying energy to it in theform of heat so as to reach its critical temperature, or in the form ofa niagnetic lield so as to reach its critical field.

In a plot of the magnetic iield as the ordinate versus temperature asthe abscissa, wherein the magnetic field is the critical field in gaussand the temperture is in K., one obtains a series of curves fordifferent materials. If at a selected temperature, i.e., 4 K., one drawsa line at right angles to the abscissa, such constant temperature linewill intersect various curves at different points. Such intersectionswill represent the magnetic iields that are necessary to drive theirrespective materials to their resistive states for the selectedtemperature of 4 K. At the temperature of 4 K, one material may requireonly fifty gauss to be `driven from its superconductive state to itsresistive state, a second may require 300 gauss, a third may require 450gauss, etc. For purposes of aiding in the discussion to follow, a hardsuperconductor is defined as that superconductor which, at a givenoperating temperature, `requires a relatively high field or current tocause it to go resistive or normal conducting, whereas a softsuperconductor is defined as that which requires a relatively low fieldor low current to cause it to go normal. It was also recognized that aclosed path or ring of superconducting material (see paragraph 2.6 ofthe above cited Shoenberg text) will act as a barrier to a magneticlield that is normal to the plane of such closed path or ring. When thatmagnetic field is increased to t-he point that it exceeds the criticalfield of the superconducting material, the latter goes resistive,permitting the penetration of the magnetic field through the ring. Itwas not known, however, that the change in resistance of thesupercon-ductor could be caused to create a heating effect which furtherincreased the resistance of the superconductive ring. If the ring couldbe caused to increase its resistance as a result of this heating, thechanged resistance of the superconductive ring would be effective toaccelerate the field, which acceleration would also heat the ring byinductive heating. The aforementioned regenerative effect and itsrecognition are exploited herein to produce more effectivesuperconductive elements and devices.

One special application of this discovery is toward the construction ofa novel cell to be used in computers whe-rein the geometry of the cellis such as to inductively store energy during the interval when thesuperconductive closed path is being driven toward its resistive state.The cell is also capable of releasing such inductively stored energy sothat the latter manifests itself as a heat generator or as a means forgenerating a rapidly changing magnetic field. This invention will dealwith instrumentalities that will make use of the heating effect, per se,to cause a very rapid switching of the supercon-ductive cell, per se, orto cause the rapid switching of other superconductor elements. Where itis desired to make use of the rapidly changing field, a suitable sensingdevice will be placed in the path of such rapidly changing magnetic eldso as to transmit an amplified signal to a suitable utilization circuit.

Wherein it .is desired to exploit the regenerative heating effect of -aswitching superconductor cell to achieve control of othersuperconductors, a hard superconductor is placed adjacent to and inheat-conducting relationship with a soft super-conductor. The softsuperconductor will require a relatively small critical magnetic fieldto make it go resistive and regeneratively heat up to give a rapidtemperature rise, say of the order of 3-15 K. l-lS millimicroseconds Theheat energy is transmitted to the hard superconductor to raise itstemperature so as to drive it resistive or normally conductive. Sincethe hard superconductor requires a relatively large critical iield todrive it resistive, the `use of a low critical field as a means fordriving a soft superconductor into its resistive state so that thelatter, when it regeneratively heats up, can switch a hardsuperconductor to its resistive state attains amplification. Arelatively small current in a drive winding associated with a softsuperconductor of the novel superconductive cell will cause the softsuperconductor to go resistive and the heat regeneratively produced willcontrol the state Iof a hard superconductor, the latter capable ofcarrying a relatively large current. Thus a small current change in asoft superconductor can be made to control the passage of a largecurrent in a hard supreconductor. It will also be shown hereinafter thata change in state of any superconductor, i.e., when the latter is madeto switch from 4its superconductive state to its resistive state so asto produce .a regenerative heating effect, can be made to controlanother superconductor regardless of the relative hardness or softnessof the two superconductors.

Accordingly it is an object of this invention to provide a novel cellemploying superconductive elements.

It is a further object to attain a superconductive cell capable of beingswitched very rapidly.

It is yet another object to provide a rapidly switching cell that isexceedingly small in size and mass so that its use in computers willserve to reduce the over-all size of such computers.

Still another object is to control the switching of a secondsuperconductor by the heat regeneratively produced when la firstsuperconductor is made to go resistive.

A further object is to employ a soft superconductor to control a hardsuperconductor, yet provide means to prevent the field produced by acurrent flowing in the hard superconductor from affecting the operatingcharacteristic-s of the soft superconductor.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawingswhich disclose, by way of example, the principles of the invention andthe best modes which have been contemplated of applying thoseprinciples.

In the drawings:

FIG. 1 illustrates an arrangement of a superconductive cell and heatcontrol trigger constructed in accordance wih the vprinciples of thepresent invention.

FIG. 2 is a cross-section of FIG. 1 taken along line 2-2 of FIG. 1.

FIG. 3 illustrates a modification of the memory cell and heat controltrigger shown in FIG. l.

FIG. 4 is a plot of the characteristic curve of critical field versus`absolute temperature for various superconductor materials.

FIG. 5 is a plot of critical current versus temperature for the samesuperconductor material of different crosssectional areas.

FIG. 6 is a plot of resistance versus the combined magnetic field andtemperature affecting a superconductor.

FIG. 7 is an equivalent circuit for the superconductor cells and heatcontrol triggers depicted in FIGS. l and 3.

FIG. 8 is a schematic diagram of an embodiment of the invention whereinthe heat control trigger of the types shown in FIGS. l and 3 areemployed to actuate a iiip-op employing superconductive elements.

FIG. 9 is a schematic diagram of a further embodiment of the inventionwherein a heat control trigger is employed to control a superconductorswitch.

FIGS. 10 and 1l are further embodiments of the invention shown in FIGS.l and 3.

Referring to FIG. 1 there is shown a superconducting fil-m or layer 1 tobe controlled, such film 1 being supported on a suitable substratum ofaluminum oxide, glass, or similar insulated self-supporting base. Aninsulator 2 of crystalline aluminum oxide is deposited oversuperconductive film 1, such insulator 2 being selected because it is agood conductor of heat or readily permits the passage of heattherethrough. Above this insulator 2 is deposited anothersuperconductive layer 3 wherein, by the use of masks or etching, holes 4and 5 are made in such superconductive layer 3. The cut-outs 4 and 5leave a very narrow cross-bar 6 in the superconductive layer 3.Separating the crossbar 6 from another superconductive layer 7 is alayer 8 of silicon monoxide or magnesium fluoride or any other suitableinsulator having relatively poor heat conducting characteristics. Whereit is desired to pack- -age the layers described hereinabove, siliconmonoxide may be used to encase all the layers to protect the latter fromdirect contact with the atmosphere. In an actual construction of thiscell shown in FIG. 1, lead, or lead containing a slight amount ofimpurities, 1500 angstroms thick was deposited on the substratum to formsuperconductive film 1, such deposition using vacuum metalizingtechniques. After a coating or layer of aluminum oxide of about 1000angstroms thick was deposited upon film 1, a second superconductivelayer of lead similar to that of layer 1 was deposited to makesuperconductive film 3, such film 3 being of the order of 800 angstromsthick. By etching or using a mask substantially semi-circular holes 4and 5 are produced in the deposited film 3 save for the cross-bar 6,such cross-bar 6 being 0.12 millimeter wide and about W10 of acentimeter in length, or about the diameter of the hole produced whenthe two semi-circular Cutouts 4 and 5 are merged. The insulated layer 8of silicon monoxide is about 800 angstroms thick and the drive wire 7was of load and was 1500 angstroms thick.

The operation of the cell of FIG. 1 as a heat control trigger will benow described with reliance being had on FIGS. 6 and 7 to aid inexplaining such operation. When a current of the order of 500 ma. havinga rise time of the order of millimicroseconds is applied to drive wire7, the magnetic field generated by the current in drive wire 7 links thegeometry of the holes 4 and 5 with that of the drive wire 7 so thatthere is an inductive coupling between the holes 4 and 5 and the drivewire 7. An electromagnetic force is generated in the holes, producingcirculating currents in the superconductive material surrounding theholes. The circulating currents, as the arrows show, would pass alongthe surface of cross-bar 6 and superconductive film 3, forming twoclosed paths about holes v4 and 5. These circulating currents, orscreening currents as they sometimes are called, set up their own fluxto oppose the tiux set up by the drive current. This takes place becausea superconductive plane acts as a barrier to the passage of fiuXtherethrough. As the initial flux attempts to penetrate thesuperconductive barrier, screening currents are set up in thesuperconductive barrier, which screening currents create their own fluxto oppose the initial iiux, so that no net fiux penetration of thesuperconductive film 1 takes place. Such screening currents are storedas magnetic fields in the inductances of the holes 4 and 5 until thescreening currents produced in the cross-bar 6 reach the criticalcurrent of cross-bar 6 and drive it into its resistive or normalconducting state. As soon as the cross-bar 6 becomes resistive, thefields built up in the inductances as well as the field generated by thecurrent in drive wire 7 punch through the cross-bar 6, since the latteris no longer capable of acting as a barrier to such fields. Not onlydoes the cross-bar 6 heat up when it goes normal conducting, but theinductively stored magnetic field as well as the increased field of thedrive wire 7 now burst through, as it were, with tremendous force acrossthe bar 6, such bursting through serving to induetively heat up bar 6,which in turn permits fiux to pass extremely rapidly through the planeof the cross-bar 6. The aforementioned regenerative effect accomplishestwo features which were hitherto unknown, namely, that (1) by properselection of the geometry of the hole and its superconductive cross-bar,as well as the rise time `of the drive current employed to create afield aliecting such cross-bar, one can obtain an inductive storage ofenergy in the form of a magnetic field which, when released, will causesuch regenerative switching of a superconductive cross-bar that thelatter will heat up an amount such that AT/At is of the order of 3-15Kelvin I-l millimicroseconds producing an exceptionally fast heatcontrol trigger; and (2) by such operation of the cell shown in FIG. l,the magnetic fields, namely, the induetively stored field and that fieldproduced by current flowing in drive wire 7 that burst through thesuperconductive plane that includes cross-bar 6 do so with such speedthat a sensing device lying in the path of such fields will produce arelatively high signal in response thereto. The cell of FIG. 1 servesboth as a heat generator or as a switching device that gives anamplified signal to a suitable sensing device.

FIG. 7 is an equivalent circuit for the heat control trigger wherein L1is considered the inductance of hole 4 and L2 is the inductance of 4hole5. The drive winding 7 is inductively coupled to cross-bar 6. Switch swis effectively closed when the cross-bar 6 is in its superconductivestate and there is no resistance R present in the cross-bar 6 circuit.There is some mutual inductive coupling between drive winding 7 andcross-bar 6 as well as between drive winding 7 and the inductancesrepresented as L1 and L2 of the holes. These mutual inductances areshown as M1, M2, and M3. As the drive current in drive wire 7 increases,a magnetic field is created around drive wire 7 which couples cross-bar6 with flux lines. These fiux lines cannot penetrate the plane thatincludes superconductive cross-bar 6, so screening currents are built upwhich circulate in the superconductive area about holes 4 and 5, suchscreening currents building up a magnetic field that opposes themagnetic field created by drive current in drive winding 7. Theinductive build-up of magnetic field in the inductances increases as thescreening currents increase, until the latter reach the critical currentfor cross-bar 6 driving the cross-bar 6 resistive. As soon as resistanceR appears in the cross-bar circuit, the opposing magnetic field createdby such screening currents lcollapses very quickly and acts as aninductive kick through resistance R (switch sw being now effectivelyopen), causing a relatively high ,2R heating of cross-bar 6 and .a sharprise in its temperature. Either the rapid heating or the rapid fiuxbreak through can be sensed, `if desired. If the drive current throughdrive wire 7 should be withdrawn before the cross-bar 6 relaxes or coolsdown sufiiciently to reach its superconductive state, then no flux willbe trapped in the areas about holes 4 and 5. If the drive current ismade to persist until the cross-bar 6 cools down to its superconductivestate and then withdrawn, flux may be trapped in the areas about holes 4and 5 so as to support circulating cur-rents in the superconductive areaabout holes 4 and 5. A copending application entitled ElectricalApparatus, Serial No. 615,830, filed October 15, 1956 by the instantapplicant was directed towards a memory cell lwhere it was particularlydesirable to obtain fiux trapping in a cell similar to the one shown inFIG. 1 of the present application so that the direction of fiux trapping(either up through a hole or down through a hole) would be indicative ofthe storage of a binary l or `a binary 0. In the present invention, theemphasis is on constructing a superconductor cell of a predeterminedgeometry so as to obtain rapid heating and fast fiux change without anyregard to the trapping of fiux.

The geometry of the cell in FIG. 1 should be such that AT N Energyavailable for heating At N Rate of heat Conduction away from the crossbar 6 into the ambient temper-ature-I-heat capacity of the masses(cross-bar 6, aluminum oxide insulation and super-conductor 1 to becontrolled by the cross-bar 6) The heat energy is made high by using adriving current having a fast rise time (of the order of 100millimicroseconds up to 500 microseconds) and the cross-bar 6 must notbe too thick so that it -will take too long to be driven into itsresistive state. For it is only when the cross-bar 6 is in its resistivestate do we get sufficient i2R loss in crossbar 6, which 1'2R lossmaintains the crossbar 6 heated so as to regeneratively drive itresistive and permit the inductively stored flux to rapidly punchthrough such cross-bar 6. Thus in FIG. 6, curve C relates to asuperconductor, for example, lead which contains a small amount ofimpurities and whose mass was too large to permit the regenerativeheating effect to take place sufficiently quickly. Whereas curve C1relates to a mass of impure lead for cross-bar 6 which permitted asufiicient rapid rise in temperature to drive it resistive, so that thecombined effects of a rapidly collapsing inductively stored magnetictield across crossbar 6 and ZR loss in the same cross-bar 6 produced anavailable supply of heat energy. Since the heat energy produced appearsfor `a very small time, of the order of l-l5 millimicroseconds, it doesnot dissipate to the surrounding bath of liquid helium in which the cellis placed. The heat capacities of the crossbar 6 as well as thesuperconductor 1 to be controlled are low, so that the geometry of thecell permits one to attain a AT/At that is of the order of 1-15millimicroseconds For the parameters selected in the illustrativeexample, an inductance of about 0.01 ithenries exists in thesuperconductive surfaces surrounding holes 4 and 5. The amount ofcurrent that can be carried by the cross-bar 6 before it reaches itscritical current would be a function of its composition and size,whereas the inductance of the cell would be effected by its geometry,such as shape of the holes 4 'and 5, disposition of the cross-bar 6 andlocation of the drive winding 7.

In FIG. 3 there is shown another way of constructing the invention ofFIG. l. The superconductive film 3 is substantially Ushaped having asoft superconductive cross-bar 6" at the arms of the U-shapedsuperconductor layer 3". The drive winding 7 is located along an edge ofthe superconductor 3 to create circulating currents therein so as toeffect soft superconductor cross-bar 6". Superconductor 1" to becontrolled is placed adjacent the soft superconductor 6". The cellgeometry of FIG. 3 isselected so as to attain rapid rise in heat nearthe soft superconductor cross-bar 6". The insulating layers have beenomitted from FIG. 3, but it is to be understood that they would beemployed Iwhen constructing the cell of FIG. 3.

Attention is now turned to FIG. 8 of the drawing to illustrate how theinstant invention may be employed to especial advantage in othersuperconductive circuits, namely, the cryotron, as described in anarticle by D. A. Buck entitled The Cryotron-A Superconductive ComputerComponent, appearing in the April 1956 issue of The Proceedings of theIRE, pages 482-493. FIG. 8 shows a cryotron flip-Hop 10 comprising acontrol winding 11 Imade of niobium or lead so that, at the temperaturesat which the fiip-fiop 10 operates, such control winding 11 will alwaysremain in its superconductive state. The control winding 11 is wrappedaround another superconductor 12, called the gate circuit, the latterbeing made of a material which can be driven to its resistive state bythe combination of two fields, namely, the field produced by the currentin control winding 11 and the field produced by the self-current fiowingin gate circuit 12. It is the vector sum of these two fields that drivesthe gate circuit 12 resistive.

The cryotron flip-flop 10 is set into operation by making one of thegate circuits 12 or 121 go normally conductive so that current enteringat input load 13 will take one parallel path in preference to the otherbefore leaving the f'lip-fiop 1t) through output lead 14. Assume thatgate circuit 12 is rendered resistive, then current Iwill fiow from lead13, through gate circuit 121, winding 15, through control winding 11 andout through lead 14. The current through control winding 11 willcontinue to create a magnetic field that will keep gate circuit 12resistive, whereas no current will flow through control winding 111 toaffect gate circuit 121. In order to fiip the current from one gatecircuit to another gate circuit, current from another source, not shown,is made to flow in winding 11 so as to drive gate circuit 121 resistive,causing the current entering the fiip-fiop 10 at lead 13 to switch togate circuit 12. This manner of switching is believed to be too slow,say of the order of aseconds.

By inserting in the gate circuits of the cryotron fiip-fiop the heatcontrol triggers of the instant invention, the cryotron flip-Hop 10 canbe switched from one path to its other path extremely rapidly, i.e., inabout l to millimicroseconds. This is accomplished by placing across-bar 6, 61 of each heat control trigger over each gate circuit 12,121, respectively, and employing a drive winding (not shown) to initiatethe regenerative heating of one of said cross-bars to selectively driveits corresponding gate circuit 12, 121 to its resistive state so thatthe flip-fiop 10 can be made to rapidly switch from one state to itsother state FIG. 9 is an example of the instant invention as it isapplied to `a superconductive switch wherein parallel paths are providedfor the current entering lead 18 and leaving at lead 19.S'uperconductive elements 20 and 21 each lie in a superconductive path.It is desired to have all the current entering at lead 18 flow int-o onepath only, say along the path that includes superconductor 21, thencross-bar 6 is driven to heat up regeneratively so as to apply its heatto the superconductive element below it, driving resistive thesuperconductive path that includes superconductive element 20 anddiverting all the current through superconductor 21. When the pathincluding element 20 cools to below its critical temperature, it willbecome superconductive again, but no current will ow in such path sincethere is no mechanism to cause the superconductive current in element 21to be withdrawn therefrom. If it is desired to divert the current fromthe right branch of FIG. 9 to the left branch of FIG. 9 then thecross-bar 61 of its heat control trigger is actuated to drive the rightbranch resistive. Although only two parallel paths are shown, it isclearly understood that more than two parallel paths may be employed.

Turning to FIG. 1, it is seen how the -heat control trigger serves alsoas an amplifier. Assume that the superconductor 1 to be controlled is ahard superconductor such as vanadium, whose Hc-T plot is shown in FIG.4, 'and the soft superconductor cross-bar 6 is lead-indium. For a givenltemperature of 4 K., a small critical field applied to cross-bar 6 willcause it to Vgo resistive but will have no effect upon vanadium since itneeds a much higher critical field to make it go resistive. But the highheat developed by the cross-bar 6 when it regeneratively goes resistivewill cause .the hard superconductor 1 to go resistive. Since thecurrent-carrying capacity of hard superconductor 1 is much higher thanthat of drive wire 7 and soft superconductor 6, a high current fiow iscontrolled by a low current fiow, resulting in amplification.

It is to be understood that it is not necessary that the hardsuperconductor be of a different material than the soft superconductor.If the superconductor to be controlled has a larger mass than thecross-bar or controlling superconductor, the former superconductor canbe considered hard with respect to the latter superconductor. FIG. 5,for example, depicts the plot of critical current versus temperature ofthe same superconductor (lead) but the cross-section or the product ofthickness and width of the superconductor is made variable, curve Xhaving the least value for its thickness-width product, curve Z havingthe highest value, and curve Y having an intermediate value. Forpurposes of practising the instant invention, the lead that has thecharacteristic plot of the Z curve is a hard superconductor with respectto the lead corresponding to the plots of curve Y and curve X.

`If desired, one may use the rapid heating that takes place when a hardsuperconductor is switched in accordance with the teachings of thisinvention to cause a soft superconductor to go resistive. This will notproduce the amplification that takes place when a soft superconductorgoes regeneratively resistive and its heat and collapsing magneticfields are used to switch a hard superconductor, but the softsuperconductor may be made to switch ex- .tremely rapidly. .Suchextremely rapid switching may 8 have particular application in computingdevices and the like.

FIGS. 10 and 1l relate to preferred embodiments of the invention whenthe latter is employed as an amplifier. Since the superconductiveelement 1 to be controlled may be carrying a current, such current willproduce a field about the element 1. This field will be in the samedirection as the field that is produced about cross-bar 6 when thelat-ter has screening currents circulating therein. To prevent the fieldof the controlled element 1 from affecting the cross-bar 6, the formeris disposed at right angles to the latter, as shown in FIG. 10, tonullify the undesired back effect of the field about element 1 uponcross-bar 6.

In FIG. l1, the element 1 to be controlled is bent back upon itself sothat opposing fields are pr-oduced by the current being carried bysuperconductive element 1. Such opposing fields cancel and prevent aback effect upon cross-bar 6. It is to be understood that these samemodifications depicted in FIGS. 10 and 1l can be applied to thatembodiment of the invention shown in FIG. 3.

The principles of superconductivity and magnetic storage have beenexploited in a novel way to produce a basic superconductive cell whosegeometry is such as to permit rapid switching of a superconductive filmor bar from its superconductive state to its resistive state in a timethat is one hundred times faster than the switching time of ferritecores. Considerably less current is required to switch suchsuperconductive cell than is required to switch such ferrite cores.Moreover the inductive release of magnetic 'fields created by screeningcurrents in the cell permits not only a rapid heating of thesuperconductive element of the cell so as to provide temperature changesof the order of 1-10 millimicroseconds but it also provides for a veryrapid break through of fields through a closed supercon-ductive path,such rapid break through providing a relatively strong signal to asensing circuit coupled to such cell. The novel cell described hereincan be employed to provide extremely rapid control to other circuits,particularly circuits employing superconductive elements. The cell,dimension-wise, can be packaged in extremely small arrays, so that theiruse in computers and the like will reduce the over-all size of t-helatter.

What is claimed is: 1. A superconductor circuit comprising: first andsecond superconductor paths extending in a parallel circuit relationshipbetween first and second terminals; first and second current supplyleads respectively connected to said first and second terminalssupplying current to said superconductor paths; first means forintroducing resistance into at least a portion of said first path for atime sufficient to cause the current from said supply leads to flow insaid second path and thereafter allow said first path to becomesuperconductive; said current fiowing in said second path beingineffective to introduce resistance into said first path and said firstand second paths remaining entirely superconluctive with said currentfiowing in said second pat second means for thereafter introducingresistance into at leas-t a portion of said second path for a timesufficient to cause the current flowing in said second .path to beswitched to said first path and thereafter allow said portion of saidsecond path to become superconductive; said current then fiowing in saidfirst path being ineffective to introduce resistance into said secondpath and said first and second paths remaining entirely superconductivewith said current fiowing in said first path. 2. The circuit of claim 1including:

References Cited bythe Examiner UNITED STATES PATENTS 2,930,908 3/1960McKeon 307-885 3,015,041

12/19611 Young 307-885 10 10 3,021,434 2/1962 Blumberg et a1 307--88-53,114,136 12/1963 Smallrnan 307-885 X OTHER REFERENCES Keister et a1.:Design of Switching Circuits, 'Vian Nostrand, 1951, page 37. TK-2831-K4.

Buck: The Cryotron, Proc. IRE, A pri1 1956, pp. 482 to 493.

ARTHUR GAUSS, Primary Examiner.

D. D. FORRER, Assistant Examiner.

1. A SUPERCONDUCTOR CIRCUIT COMPRISING: FIRST AND SECOND SUPERCONDUCTORPATHS EXTENDING IN A PARALLEL CIRCUIT RELATIONSHIP BETWEEN FIRST ANDSECOND TERMINALS, FIRST AND SECOND CURRENT SUPPLY LEADS RESPECTIVELYCONNECTED TO SAID FIRST AND SECOND TERMINALS SUPPLYING CURRENT TO SAIDSUPERCONDUCTOR PATHS; FIRST MEANS FOR INTRODUCING RESISTANCE INTO ATLEAST A PORTION OF SAID FIRST PATH FOR A TIME SUFFICIENT TO CAUSE THECURRENT FROM SAID SUPPLY LEADS TO FLOW IN SAID SECOND PATH ANDTHEREAFTER ALLOW SAID FIRST PATH TO BECOME SUPERCONDUCTIVE; SAID CURRENTFLOWING IN SAID SECOND PATH BEING INEFFECTIVE TO INTRODUCE RESISTANCEINTO SAID FIRST PATH AND SAID FIRST AND SECOND PATHS REMAINING ENTIRELYSUPERCONDUCTIVE WITH SAID CURRENT FLOWING IN SAID SECOND PATH, SECONDMEANS FOR THEREAFTER INTRODUCING RESISTANCE INTO AT LEAST A PORTION OFSAID SECOND PATH FOR A TIME SUFFICIENT TO CAUSE THE CURRENT FLOWING INSAID SECOND PATH TO BE SWITCHED TO SAID FIRST PATH AND THEREAFTER ALLOWSAID PORTION OF SAID SECOND PATH TO BECOME SUPERCONDUCTIVE; SAID CURRENTTHEN FLOWING IN SAID FIRST PATH BEIG INEFFECTIVE TO INTRODUCE RESISTANCEINTO SAID SECOND PATH AND SAID FIRST AND SECOND PATHS REMAINING ENTIRELYSUPERCONDUCTIVE WITH SAID CURRENT FLOWING IN SAID FIRST PATH.